New tool maps dengue's climate spread

Scientists have developed a method to predict the spread of the dengue-carrying Aedes aegypti mosquito as the climate changes.

Australian and US researchers identified the key factors that determine where A. aegypti mosquitoes can live.

These include aspects of the mosquito's biology such as the ability of its eggs to tolerate drying out, environmental factors such as temperature, and factors that in part depend on human behaviour, such as the availability of standing water for the mosquito to lay its eggs in.

By combining these factors with climate change projections, they found that suitable habitats for A. aegypti will increase in the next 40 years in Australia — into areas that had previously been hostile to the mosquito.

The model can be used anywhere with A. aegypti populations, particularly the tropical and subtropical countries where dengue is a problem, the researchers say.

"The software which developed this prediction is called 'Niche Mapper'. This system is applicable to any geographical situation in the world, especially in developing countries still badly hit by dengue fever such as Indonesia," says Ary Hoffmann, a co-author of the study and a fellow in the genetics and zoology departments of the University of Melbourne, Australia.

And the model can also be used to predict the spread of any disease vector, says Hoffmann. It is simply a case of working out which parameters are appropriate to the insect you want to study.

But the researchers are keen to emphasise that the predicted spread of dengue mosquitoes is not inevitable.

While humans cannot control the ability of mosquitoes to evolve and adapt to different environmental conditions, they can reduce potential A. aegypti habitats, says Hoffman.

The mosquitoes need standing water in which to lay their eggs, and they are attracted to artificial water containers, so interventions such as covering water containers will decrease the spread of the mosquito, he says.

Routine screening of water storage containers should also be carried out, and in some places predators can be added to water — in paddy fields and fishponds for example.

The study was published last month (28 January) in Functional Ecology.